Really need help :(

[Thorsson]

No, RAM B is dead by the sounds of it. RMA the fokker.

[Pob255]

yep sounds like the ram is bad
RMA both that and the psu (once you try both slots pci-e and cables, if it's only a duff cable then contact corsair and they'd send you a new one) however if there's a problem with the PCI-E on that PSU then RMA it, no point paying for something that only half works, yes you have a way around it but that's not the point.
You paid for a psu with working pci-e power and a nice 10year warranty.
Also you should post on the Corsair Care section of these forums.

[Bounty_Bam]

Really odd. as you know, RAM B wont boot.

But when I (I know I shouldn't of) insert RAM B just after the POST screen on boot up, my computer runs and says 4.00GB RAM. But when i reboot its back to not booting again. Doesn't this mean that RAM B ISN'T dead??

[Thorsson]

RAM B doesn't boot. That the motherboard can recognise it doesn't change that basic fact. Plenty of bad RAM will boot, just cause BSODs and/or other problems. Be thankful that yours is so clear cut and RMA it.